The exact start and end of the toddler period is not precisely defined. Most pediatricians and organizations consider children to be toddlers when they are between 12 and 36 months, and some groups use the term through a child's fourth birthday.
The term toddler comes from the toddling gait of a child who is just learning to walk. Because the ability to toddle develops at different ages for different children, the onset of toddlerhood may vary. Babies who learn to walk before their first birthday might be called toddlers at 10 or 11 months of age, while late bloomers might not begin to toddle until a few months after their first birthday. By age 4, all children are generally considered to be preschoolers, not toddlers.